(VAR f h t x )
(RULES 
        app(app(twice, f), x) -> app(f, app(f, x))
        app(app(map, f), nil) -> nil
        app(app(map, f), app(app(cons, h), t)) -> app(app(cons, app(f, h)), app(app(map, f), t))
        app(app(fmap, nil), x) -> nil
        app(app(fmap, app(app(cons, f), t_f)), x) -> app(app(cons, app(f, x)), app(app(fmap, t_f), x))
        
)